Energy absorbers

ABSTRACT

A railway buffer capsule comprising a hollow cylindrical plunger slidably mounted in a cylinder. The cylinder is closed at one end. The plunger is closed at its outer end, and in its inner end is formed a fixed area orifice of flow restricting dimensions. A floating piston slides in the bore of the plunger and separates a liquid reservoir from the remainder of the interior of the plunger which comprises a gas containing space. A stepped piston has its larger diameter exposed to pressure in the reservoir and its smaller diameter end adapted to seat and close the orifice and be exposed to compression chamber pressure. The combination of the stepped piston and the orifice is a multiplier valve which multiplies the resistance of the compressed gas to lengthwise compression of the buffer.

DESCRIPTION

1. Field of the Invention

This invention relates to energy absorbers of the kind which comprise acylinder and a hollow plunger slidable in the cylinder, the plungerhaving its interior divided into a gas containing space and a liquidreservoir by a movable wall and being provided with means whereby theliquid reservoir communicates with a liquid compression chamber formedwithin the cylinder outside the plunger, liquid displaced from thecompression chamber into the reservoir by lengthwise compression of theabsorber acting on the movable wall to displace it and thereby causecompression of gas within the gas containing space such that lengthwisecompression of the absorber is resisted by compressed gas within the gascontaining space which also provides a recoil force, there being liquiddamping means which provide further resistance to compression of theabsorber and damp the recoil force under certain conditions ofoperation. Such an energy absorber shall be referred to as "an energyabsorber of the kind referred to" throughout the remainder of thisspecification.

2. Description of the Background Art

DE-B-1109206 discloses the use in an energy absorber of the kindreferred to of a spring-closed pressure relief valve which is operableto open against the spring loading to allow displacement of liquid fromthe compression chamber into the liquid reservoir through an orificewhich serves as the liquid damping means, when the liquid pressureacting on the obturating member of the pressure relief valve to open itreaches a certain threshold pressure which is many times higher than gaspressure within the gas containing space. The spring loading of theobturator of the pressure relief valve is applied by a stack of springwashers and is substantial. Liquid pressure loading on that obturator isinsignificant compared to the load exerted by that stack of springwashers. That is so also with the energy absorber of the kind referredto disclosed by DE-A-3613677 which also includes a spring closed valvewhich is opened by liquid pressure in the compression chamber to allowdisplacement of liquid from the compression chamber to the liquidreservoir. The damping characteristics of the latter energy absorber aredetermined by the level of prestressing of the springs.

In order to provide the desired velocity dependent characteristics, ithas always been thought necessary for the liquid damping means tocomprise an orifice arrangement of flow restricting dimensions, theeffective area of which is varied with relative telescopic movementbetween the hollow plunger and the cylinder, the effective areadiminishing as the energy absorber contracts and increasing as itextends.

GB-A-982641 and GB-A-1266596 disclose examples of "an energy absorber ofthe kind referred to" which forms part of a side buffer for use onrailway vehicles to absorb shock loads transmitted from one vehicle toanother during acceleration and deceleration of a train, or during wagonimpacts in marshalling yards and which, in the conventional manner,incorporate a profiled pin which, with inward movement of the plunger,provides increasing restriction of an orifice through which the liquidreservoir communicates with the liquid compression chamber.

SUMMARY OF THE INVENTION

An object of this invention is to provide an energy absorber of the kindreferred to which is less expensive to manufacture but which will havesubstantially the same `so-called` static and dynamic performancecharacteristics when used in a side buffer as an energy absorber whichis similar to those disclosed by GB-A-982641 and GB-A-1266596.

Rather than using a variable area orifice arrangement of flowrestricting dimensions as is conventional, by this invention we use afixed area orifice of flow restricting dimensions as the liquid dampingmeans of an energy absorber of the kind referred, in combination with amultiplier valve which cooperates with that orifice to multiply theresistance of the compressed gas within the gas containing space tolengthwise compression of the absorber.

According to this invention there is provided an energy absorber of thekind referred to, wherein the means whereby the liquid reservoircommunicates with the liquid compression chamber comprises an orificeformed in the plunger and the liquid damping means consist solely inthat orifice and a valve which is operable to inhibit passage of liquidthrough the orifice from the compression chamber to the reservoirchamber when a force which is less than a predetermined threshold forceis applied to urge the plunger axially into the cylinder and to open toallow displacement of liquid from the compression chamber to thereservoir chamber through the orifice when a force which is greater thanthe predetermined threshold force is applied to urge the plunger intothe cylinder chamber, wherein the valve comprises an obturating memberwhich is a differential area piston, the larger surface area of whichdifferential area piston is exposed to liquid in the reservoir chamberand the smaller diameter end portion of which differential area pistonis adapted to seat on the perimeter of the orifice when the valve closesthat orifice.

Theoretically use of a fixed area orifice of flow restricting dimensionsas liquid damping means of an energy absorber should not be satisfactorybecause it should function like a dashpot with a single hole and as suchit should not provide effective metering of the flow of liquid displacedfrom the compression chamber to the liquid reservoir. However, when usedin combination with gas in the gas containing space of an energyabsorber of the kind referred to, and with the differential area pistonthat interacts with the fixed area orifice of flow restrictingdimensions as a multiplier valve which multiplies the action of the gasin the gas containing space, the resultant effect of that combination isa performance characteristic which is a surprisingly good approximationto the performance characteristics of a typical energy absorber of thekind referred to which incorporates the conventional arrangement of aprofiled pin which with inward movement of the plunger, providesincreasing restriction of the orifice through which liquid is displacedfrom the compression chamber to the liquid reservoir.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

A railway side buffer in which this invention is embodied will bedescribed now by way of example with reference to the accompanyingdrawings, which are given by way of illustration only, and thus are notlimitative of the present invention, and of which:

FIG. 1 is a transverse cross-section of the buffer;

FIG. 2 is an enlarged cross-section detail on the line II--II of FIG. 1;and

FIG. 3 is an end view of the valve shown in FIG. 2 as seen in thedirection of arrow A in FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a railway buffer capsule comprising a hollow cylindricalplunger 10 slidably mounted in a cylinder 11. The cylinder 11 is closedat one end 12. The plunger 10 is closed at its outer end 13 to which abuffer plate 14 is fixed and at its inner end it has an end wall 15 inwhich is formed a central aperture 16.

A floating piston 17 slides in the bore of the plunger 10 and separatesa liquid reservoir 18, which is formed within the plunger 10 adjacentthe inner end wall 15, from the remainder of the interior of the plunger10. The interior of the plunger between the floating piston 17 and theouter end wall 13 comprises a gas containing space 19 which is filledwith compressed gas, such as nitrogen, on assembly of the buffer.

FIG. 2 shows central aperture 16 is stepped, having a tapped inner boreportion 20 at its end which is nearer to the floating piston 17 and asmaller diameter bore portion 21 at its end nearer the closed outer endwall 12 of the cylinder 11, the smaller diameter bore portion 21 formingan orifice of flow restricting dimensions. An annular valve body 22, isscrewed into the tapped, bore portion 20 so that its end face abuts theend wall of the bore 20. The bore of the annular valve body 22 isstepped. A smaller diameter portion 23 of the stepped bore is nearer tothe smaller diameter bore portion 21 than is the larger 24 of the twobore portions of the stepped bore of the valve body 22.

A solid stepped or differential area piston 25 is a sliding fit in thestepped bore of the annular valve body 22 and its smaller diameter end26 is adapted to seat in the orifice 21 so as to serve as an obturatingmember. Surrounding the solid stepped piston 25 at its smaller end is anannular chamber 28 formed between the valve body 22 and the step betweenthe orifice 21 and the tapped bore portion 20. Communication means, forthe flow of liquid from the compression chamber 32 via the annularchamber 28 to the reservoir chamber 18 is formed in the valve body 22 bypassages 27. The solid stepped piston 25 slides in the stepped throughbore in the valve body 22. The annular surface area of the largerdiameter end of the stepped piston 25 is several times larger than thecross-sectional area of the orifice 21. The outer end of the largerdiameter portion 24 is closed by an end plug 29. Damping holes 30 areprovided in the end plug 29 to prevent damage to the stepped piston 25.

FIG. 1 shows a non-return valve 31 which allows one-way flow from thereservoir chamber 18 to a compression chamber 32 which is formed in thecylinder 11 between the closed end wall 12 and the hollow plunger 10.

In use, the cylinder 11 is mounted on structure of a railway vehicle.When the buffer is unloaded, the compressed gas will have caused theplunger 10 to have taken up the position within the cylinder 11 in whichthe liquid pressure loading across its end wall 15 is balanced and thefloating piston 17 to have taken up the position within the plunger 10in which the fluid pressure loading across it is balanced. Thedifferential area piston 25 will be seated to close the orifice 21 inthe end wall.

In the event of the buffer being compressed by the application of animpact force to the buffer plate 14 whilst the buffer is stationery,there will be an instantaneous increase in the pressure within thecompression chamber 32 because the plunger 10 is sealed by thedifferential area piston portion 25 being seated. When the appliedimpact force reaches a certain predetermined level (say 10 KN) thepressure in the compression chamber 32 will rise sufficiently above thatin the reservoir chamber 18 to unseat the differential area piston 25.Hence liquid will be displaced from the compression chamber 32 into thereservoir chamber 18 so that the floating piston 17 will be displaced toreduce the volume of the gas containing space 19 and increase thepressure of gas therein and thus to increase the recoil force.

Energy will be absorbed by displacement of the liquid through thedifferential area piston 25 depending on the rate of further compressionof the buffer. Either the differential area piston 25 will remainunseated so that displacement of liquid through it from the compressionchamber 32 to the reservoir chamber 18 will continue or, if the furthercompression is slow, the differential area piston 25 may act as ashuttle valve being alternately reseated and unseated, further suchliquid displacement through it occurring when it is unseated.

Compression of the buffer stops when the energy of the impact force hasbeen absorbed. When the applied load is released so that the buffer canbe extended the gas in the gas containing space 19 expands to urge thefloating piston 17 towards the end wall 15 in the usual way. Liquid isdisplaced from the reservoir chamber 18 via the non-return valve 31 intothe compression chamber 32 which urges the plunger 10 out of thecylinder 11 in the usual way.

The basic energy absorber capsule comprising the hollow plunger 10 andthe cylinder 11 may be used in other forms of energy absorber. In oneexample, it may be incorporated in railway drawgear which may comprisean end of car coupler.

A consequence of the incorporation of the multiplier valve whichcomprises the combination of the differential area piston 25 and thefixed area orifice 21 is that the pressure to which the gas containingspace 19 is inflated need not be so high as would otherwise be necessarywhich is advantageous from the safety viewpoint.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded is adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

We claim:
 1. An energy absorber comprising a cylinder and a hollowplunger slidable in the cylinder, the plunger having an interior dividedinto a gas containing space and a liquid reservoir by a movable wall andbeing provided with means whereby the liquid reservoir communicates witha liquid compression chamber formed within the cylinder outside theplunger, liquid displaced from the compression chamber into thereservoir by lengthwise compression of the absorber acting on themovable wall to displace the wall and thereby cause compression of gaswithin the gas containing space such that the lengthwise compression ofthe absorber is resisted by compressed gas within the gas containingspace which also provides a recoil force, there being liquid dampingmeans which provide further resistance to compression of the absorberand damp the recoil force under certain conditions of operation, and inwhich the means whereby the liquid reservoir communicates with theliquid compression chamber comprises an orifice formed in the plungerand the liquid damping means consist solely in that orifice and a valvewhich is operable to inhibit passage of liquid through the orifice fromthe compression chamber to the reservoir chamber when a force which isless than a predetermined threshold force is applied to urge the plungeraxially into the cylinder, the valve being openable for displacement ofliquid from the compression chamber through the orifice when a forcewhich is greater than the predetermined threshold force is applied tourge the plunger into the liquid compression chamber, the valvecomprising a stepped piston which has two ends and an intermediateportion which is slidably fit in structure of the plunger between saidcompression chamber and the reservoir, the diameter of the steppedpiston being smaller at one of its ends than at the other of its ends,the smaller diameter end of the piston serving as an obturating memberseatable on a valve seat formed around the orifice to thereby close theorifice and the larger diameter end being exposed to liquid in thereservoir chamber.
 2. The energy absorber according to claim 1 which isincorporated in a railway side buffer.
 3. The energy absorber accordingto claim 1, further comprising a buffer plate mounter on the plunger atan end opposite the orifice, force being applied to the energy absorberat the buffer plate.
 4. The energy absorber according to claim 1,wherein the stepped piston is mounted in a valve body mounted on an endof the plunger adjacent the orifice, the valve body having a steppedbore with a smaller diameter bore portion and a larger diameter boreportion.
 5. The energy absorber according to claim 4, wherein the valvebody further has an annular chamber surrounding the smaller end of thepiston, the annular chamber being adjacent the orifice.
 6. The energyabsorber according to claim 5, further comprising a plurality ofpassages formed in the valve body from the annular chamber to thereservoir, liquid being flowable from the compression chamber throughthe orifice, through the annular chamber and through the plurality ofpassages when the valve is opened.
 7. The energy absorber according toclaim 6, wherein the plurality of passages each have a longitudinal axisand the orifice has a longitudinal axis, the longitudinal axes of thepassages being nonperpendicular and nonparallel to the longitudinal axisof the orifice.
 8. The energy absorber according to claim 1, furthercomprising a passage With a non-return value provided on an end of theplunger, liquid being flowable from the reservoir to the compressionchamber through the passage in the end of the plunger but the non-returnvalve preventing flow of liquid from the compression chamber to thereservoir through the passage in the end of the plunger.
 9. An energyabsorber comprising:a cylinder and a hollow plunger slidable in thecylinder, the plunger having an interior and a movable wall beingprovided in the interior of the plunger, the movable wall dividing theinterior into a gas containing space and a liquid reservoir, thecylinder having a liquid compression chamber therein; means forcommunicating the liquid reservoir with the liquid compression chamber,the means for communicating comprising an orifice formed in the plunger,liquid being displacable from the liquid compression chamber into thereservoir by lengthwise compression of the energy absorber acting on themovable wall to displace the movable wall and thereby cause compressionof gas within the gas containing space such that the lengthwisecompression of the energy absorber is resisted by compressed gas withinthe gas containing space which also provides a recoil force; liquiddamping means for further resisting compression of the energy absorberand damping recoil force when a predetermined force acts on theabsorber, the liquid damping means comprises a valve for inhibitingpassage of liquid through the orifice from the compression chamber tothe reservoir chamber when a force which is less than a predeterminedthreshold force is applied to urge the plunger axially into thecylinder, the valve being openable for displacement of liquid from thecompression chamber through the orifice when a force which is greaterthan the predetermined threshold force is applied to urge the plungerinto the liquid compression chamber, the valve comprising a steppedpiston having first and second ends and an intermediate portion which isslidably fit in the plunger between said compression chamber and thereservoir, a diameter of the first end of the piston being smaller thana diameter of the second end of the piston, the first end of the pistonserving as an obturating member seatable on a valve seat formed aroundthe orifice to thereby close the orifice, the second end of the pistonbeing exposed to liquid in the reservoir chamber.
 10. The energyabsorber according to claim 9, wherein the liquid compression chamber ofthe cylinder is outside the plunger.
 11. The energy absorber accordingto claim 9, further comprising a valve body mounted on an end of theplunger, the orifice being in an end of the plunger and the valve beingcontained entirely Within the valve body and the end of the plunger. 12.The energy absorber according to claim 9, wherein the valve is mountedwithin the plunger and is movable with the plunger.
 13. The energyabsorber according to claim 9, wherein the valve is out of contact withthe cylinder.
 14. The energy absorber according to claim 9, wherein thecylinder has a closed end forming the liquid compression chamber, theorifice only being closed by the stepped piston, the stepped pistonbeing at an end of the Orifice which is distal from an end of theorifice closest to the closed end of the cylinder.
 15. The energyabsorber according to claim 9, further comprising a buffer plate mounteron the plunger at an end opposite the orifice, force being applied tothe energy absorber at the buffer plate, the energy absorber beingincorporated in a railway side buffer.
 16. The energy absorber accordingto claim 9, wherein the stepped piston is mounted in a valve bodymounted on an end of the plunger adjacent the orifice, the valve bodyhaving a stepped bore with a smaller diameter bore portion and a largerdiameter bore portion.
 17. The energy absorber according to claim 16,wherein the valve body further has an annular chamber surrounding thefirst end of the piston, the annular chamber being adjacent the orifice.18. The energy absorber according to claim 17, further comprising aplurality of passages formed in the valve body from the annular chamberto the reservoir, liquid being flowable from the compression chamberthrough the orifice, through the annular chamber and through theplurality of passages when the valve is opened.
 19. The energy absorberaccording to claim 18, wherein the plurality of passages each have alongitudinal axis and the orifice has a longitudinal axis, thelongitudinal axes of the passages being nonperpendicular and nonparallelto the longitudinal axis of the orifice.
 20. The energy absorberaccording to claim 9, further comprising a passage with a non-returnvalve provided on an end of the plunger, liquid being flowable from thereservoir to the compression chamber through the passage in the end ofthe plunger but the non-return valve preventing flow of liquid from thecompression chamber to the reservoir through the passage in the end ofthe plunger.